The invention relates generally to elevator control systems and more specifically to an electrical control system wherein load cells provide data regarding elevator car loading and a microprocessor provides a signal corresponding to the torque level required to maintain the elevator car stationary subsequent to release of the brake and prior to initiation of a trip drive sequence.
The automatic control of elevators through microprocessors of various sizes and complexities is well documented in the patent literature. Various subroutines based upon historic elevator loading, for example, may be utilized to assign elevators to specific floors and general upward and downward operational patterns to achieve optimum elevator utilization and minimum passenger delay. Systems generally intended to provide such features in multiple car installations are disclosed in U.S. Pat. Nos. 4,603,387, 4,591,985, 4,536,842, 4,452,341 and 4,427,095.
As a means of determining elevator loading on a real time basis, for achieving, among other goals, optimum utilization of elevator resources, entails determining on a weight basis the loading of individual elevator cars. Such loading is typically achieved for example, U.S. Pat. No. 4,330,836 teaches the use of transducers for sensing the actual weight of the passengers within an elevator car. U.S. Pat. No. 4,380,275 teaches the use of such passenger weight data as an input to a prioritizing elevator control system. Likewise, U.S. Pat. No. 4,623,041 teaches the use of such elevator car weight information to improve the acceleration and deceleration performance of the elevator car.
One of the most and possibly the most critical portion of a elevator trip is the moment between release of the brake and the beginning of ascent or descent. If drive torque is applied to the motor before the brake is released the elevator car will typically undergo a jerk or rapid acceleration when the hold back torque of the releasing brake is overcome by the drive torque of the motor. Such performance may vary from un-noticeable through unpleasant to unacceptable. Conversely, if drive power to the elevator motor is delayed until the brake is fully released, the car may momentarily translate up or down depending upon the relationship between the instantaneous car weight and the counterweight. When such translation is in the same direction as the controlled and driven direction of the elevator car, it may likewise vary from the un-noticeable to the mildly annoying. However, when such translation is in the opposite direction of the controlled and driven direction of the elevator car, such performance is generally viewed as disconcerting and unacceptable. Since the momentary free translation of the car will effectively be random, depending on the difference between the car loading and the counterweight, such pre-travel will likewise be random.
In view of the foregoing, it is apparent that even the brief interval between the release of the brake and the application of drive energy to an elevator motor demands consideration. The method and apparatus of the present invention is so directed.